1. Field of the Invention
This invention pertains in general to vehicle axle assemblies and, more particularly, to an improved method for manufacturing a banjo-type axle housing for such an axle assembly.
2. Description of the Prior Art
Axle assemblies are well known structures that are in common use in most vehicles. Such axle assemblies include a number of components, which are adapted to transmit rotational power from an engine of the vehicle to the wheels thereof. Typically, an axle assembly includes a differential assembly that is rotatably supported within a non-rotating carrier. The differential is connected between an input drive shaft extending from the vehicle engine and a pair of output axle shafts extending to the vehicle wheels. The axle shafts are contained in respective non-rotating beam portions, which are secured to the carrier. Thus, rotation of the differential by the drive shaft causes corresponding rotation of the axle shafts. The carrier and the beam portions form an axle housing for these drive train components of the axle assembly, inasmuch as the differential and the axle shafts are supported for rotation therein.
Axle housings are generally classified into two basic types. The first axle housing type is a unitized carrier construction, commonly referred to as a Salisbury or Spicer type axle assembly. In this structure, the carrier (which houses the differential assembly) is directly connected to the two beam portions (which house the rotatable axle shafts). An opening is provided at the rear of the carrier to permit assembly of the differential therein. A cover closes this opening during use. Unitized carrier axle housing constructions of this type are economical to manufacture and are readily adaptable for a variety of vehicles.
The second axle housing type is a separable carrier construction. In this structure, the axle beam portions are connected together by a central portion of the axle housing that is formed separate and apart from the differential carrier. This central portion is generally hollow and cylindrical in shape, having a large generally circular opening formed therethrough. During assembly, the differential is first assembled within the carrier, then the carrier is secured to the central member. The overall shape of this type of axle housing (i.e., the generally round shape of the central portion and the elongated beam portions extending therefrom) generally resembles the shape of a banjo musical instrument. Hence, this type of axle housing is commonly referred to as a banjo type axle housing. Banjo type axle housings are advantageous because the carrier and differential can be removed from the axle assembly for service without disturbing the other components thereof.
In the past, several methods have been employed to form banjo type axle housings. A first known method involved forming the hollow cylindrical central member and the two beam portions as three separate pieces. The beam portions were then secured to the central member by welding or other means to form the housing. A second known method involved forming the entire housing from a single tubular blank. A hole was cut through the center of the blank, then formed into the hollow cylindrical central member, while the opposed end portions of the blank extended outwardly therefrom to form the beams. A third known method involved forming the central member integrally from the ends of the two beams. This was accomplished by splitting one end of each of the two beam portions, spreading the two split ends apart, and securing the two spread ends together to form the hollow cylindrical central member.
A fourth and one of the most common methods for manufacturing the banjo type axle housings involves forming two opposite halves of the axle housing by stamping or forging from a pre-cut blank of sheet steel. Next, the two axle housing halves are then welded along mated horizontal edges, and then the axle assembly is completed in a known manner. The described method is well known in the art and disclosed in a number of U.S. Patents, e.g. U.S. Pat. Nos. 4,921,159 and 2,674,783, incorporated herein by reference.
The above fourth method for manufacturing the banjo type axle housings is relatively simple and efficient. However, tooling used for stamping the axle housing halves is very expensive. Moreover, when a number of axle housings of various sizes are produced, a corresponding number of different metal forming apparatuses has to be employed that requires rather large tooling expenses.
While the above-described known methods have been used successfully to form banjo type axle housings, it has been found that all require large tooling expenses, especially when a number of different axle housing designs is produced by the same manufacturer.
Therefore, it would be desirable to provide an improved method for forming a banjo type axle housing which employs a common metal forming apparatus and a single size of the metal stamping for producing different axle housing designs, thus considerably reducing cost of manufacture.
It is an object of the present invention to provide an improved method for manufacturing a banjo-type drive axle housing for a motor vehicle, including an enlarged central portion defining a hollow interior adapted for housing a differential assembly therein, and a pair of sleeve-like axle beam portions outwardly laterally extending from opposite sides of the center portion for housing axle shafts. The central portion has a front carrier opening and a rear opening formed theretrough. The axle beam portions of the axle housing of the present invention are generally rectangular in cross-section to withstand torsional and vertical loading strains and stresses. The rectangular cross-section of the axle beam portion is known in the art as a box-section, and is characterized by a height of the box-section and its width.
The present invention is directed to a method for manufacturing of a range of banjo-type axle housings of selective box-sections of the axle beam portions and size of the openings in the central portion thereof.
The method, according to the present invention, is performed in the following manner.
First step is the operation of forming the substantially identical upper and lower channel-shaped half members, such as by stamping or forging, from a blank metal sheet. Each of the housing half members has a substantially U-shaped cross-section along entire length thereof with radially extending sidewalls.
Next step is to select a desired box-section of the axle beam portions of the axle housing corresponding to a required axle housing vertical load rating, and a desired size of the openings in the central portion of the axle housing corresponding to a required axle housing torque rating.
Then, if necessary, proper portions of the sidewalls of the axle beam half portions of both the upper and lower housing half members are trimmed so as to provide the desired box-section of the axle beam portions of the axle housing when assembled. Also, if necessary, proper portions of the sidewalls of the banjo half portion of both the upper and lower housing half members are trimmed so as to provide the desired size of the openings in the central portion of the axle housing when assembled.
Finally, the trimmed matched upper and lower housing half members are secured to each other, preferably by welding along mating horizontal edges, thus providing the desired box-section of the axle beam portions and the openings in the central portion 12 of the axle housing.
Therefore, the present invention allows to manufacture banjo type axle housings having selective height of the box-section of the axle beam portions, and selective size of the carrier opening and/or the rear opening of the central portion determined by the specific requirements of vehicle manufacturers, using a common metal forming apparatus and a single size of the metal stamping. Thus, the method for manufacturing a banjo-type drive axle housing according to the present invention, allows significantly reduced tooling expenses and provides a substantially more flexible manufacturing process.